A currently used finishing process for cold forming teeth on an external gear is to roll the teeth on a gear rolling machine. This process involves rolling a gear blank, after having been hobbed, between a pair of rotating gear dies that have die teeth on their outer surfaces. The gear blank is engaged between the rolling dies, which move linearly closer together while rolling to gradually finish form the teeth. The linear movement is limited by a fixed stop or linear displacement sensor that ceases the linear motion of the gear dies when a predetermined position is reached. This process results in a fixed, as rolled, tooth thickness.
Because of the variations inherent in hobbing when rough forming the gear teeth, the hobbed part tooth thickness varies, and the amount of material on a gear blank that is moved by the gear dies also varies between parts. This current process produces good results only if incoming roughed parts are held within a tight size tolerance range. If not, excessive force levels can be generated for these out-of-tolerance blanks, which allows unnecessary force to be transferred into the stop of the rolling machine. Further, when rolling a gear, the tooth profile will vary with the amount of material moved. Consequently, the size variation of input parts can cause inaccurately produced forms with current position feedback systems used with the roll finishing process.
It has been determined that, if the same amount of material is moved on each part rolled, each part will have a constant involute profile, which causes less tooth-to-tooth to-tooth profile variability. Further, if a consistent amount of material is moved during the roll finishing operation, excessive force levels on the rolling machine can be avoided.
A different type of rolling machine, generally used for the distinct purpose of rolling flat sheets of stock to a desired thickness, uses continuous die force monitoring on a series of pairs of smooth rollers. It forms the flat, smooth material by slowly thinning it out as it passes through each pair of rollers. However, these machines are designed and used for the purpose of providing a flat smooth sheet by rolling linearly through the series of roller pairs oriented ninety degrees from the flat sheet, and do not necessarily provide the type of apparatus and monitoring necessary to finish form the involute surfaces of a cylindrically shaped external gear, or have the same concerns with the amount of material moved to maintain a proper tooth profile regardless of the tolerances of a hobbing process.